An electrochemical cell employing lithium as the anode active metal and thionyl chloride (SOCl.sub.2) as both the electrolyte solvent and the liquid cathode and lithium tetrachloro aluminate (LiAlCl.sub.4) as the electrolyte salt has been known as a potential power source for consumer applications such as pacemakers, electronic devices, and watches, and for many military applications such as missiles and torpedoes. The attractiveness of this electrochemical cell results from its high cell voltage, usually between 3 V and 3.6 V depending upon the power drain rate, and its high energy density, up to 300 watt-hours per pound in D-size cells.
The choice of the electrolyte salt in the aforementioned cell is an important criterion for its acceptable performance. Generally speaking, the electrolyte salt helps impart conductivity to the electrolyte and maintain proper Li.sup.+ ion transport in the cell during cell discharge. An important drawback of the cell when it contains LiAlCl.sub.4 as the electrolyte salt is that the cell exhibits an unacceptable voltage depression to less than 2.0 V after storage for extended periods of time, especially at elevated temperatures. This voltage depression, known in the art as voltage delay, is caused by an insulating film which forms on the Li anode in a continuous manner with storage.
The role of the electrolyte salt in controlling the growth of the insulating film is evidenced by prior work which shows varying degrees of lessening of the problems when LiAlCl.sub.4 is replaced by other salts. In U.S. Pat. No. 4,020,240, lithium cloroborate (Li.sub.2 B.sub.10 Cl.sub.10) was claimed as a substitute for LiAlCl.sub.4 for alleviating voltage delay. Recent published work (A. N. Dey and J. Miller, J. Electrochem. Soc. 126, 1445 (1979)) on the performance of lithium-SOCl.sub.2 cells which utilize Li.sub.2 B.sub.10 Cl.sub.10 electrolyte salt and which were stored at 70.degree. C. for extended periods of time, indicate some loss in cell capacity with storage as a result of electrolyte instability. Another prior work (J. P. Gabano and D. Lenfant in "Proceedings of the Symposium on Battery Design and Optimization," The Electrochemical Society, V 79-1, p. 348 (1979)) which claims alleviation of voltage delay in the aforementioned electrochemical cell utilizes an electrolyte composition derived from the direct reaction of 1 mole of Li.sub.2 O and 2 moles of AlCl.sub.3 in SOCl.sub.2, such that the resulting solution has a 1 molar lithium ion concentration. In that publication it is claimed that the electrolyte salt is the complex, 2Li.sup.+ [AlCl.sub.3 --O--AlCl.sub.3 ].sup.-2.
Because of the crucial role of the electrolyte composition and particularly that of the electrolyte salt in deciding the performance characteristics of the Li-anode-SOCl.sub.2 electrochemical cell, novel and effective electrolyte compositions and/or electrolyte salts are desirable. In a recent patent (U.S. Pat. No. 4,117,329), salts of the general formula, M(ZX.sub.4).sub.n, exemplified by LiGaCl.sub.4, have been claimed as possible substitutes for LiAlCl.sub.4.